The invention relates to a method of trimming precision resistors, which resistors each include an insulating core coated with a suitable conductive film, end caps or other terminations being applied thereto.
A known method of trimming the above resistors includes cutting slots or grooves into the surface thereof which increases the resistance through the resistor by extending the resistance path. This method is generally effective for trimming precision resistors to within 0.5% to 1.0% of a specified electrical resistance.
However, when greater precision is desired, for example 0.25% tolerance or better, it becomes exceedingly difficult to accurately find and continue the original groove and to accurately control the length of the groove so that the final resistance through the resistor is within the desired tolerance of the specified resistance without overshooting the specified resistance. It should be noted that the known methods of trimming precision resistors only increase the resistance through the resistors and that once the specified resistance is exceeded, there is no practical way to reduce the resistance through the resistor.